The present invention relates generally to the storage and retrieval of data within magnetic media. In particular, the present invention relates to the placement of high magnetic moment material at the writer pole tip, a novel writer head design incorporating high magnetic moment material of the pole tip, and the process for manufacturing the novel writer head.
A typical magnetic head consists of two portions: a writer portion for storing magnetically encoded information on a magnetic media, for example a disc, and a reader portion for retrieving the magnetically encoded information from the disc. The reader portion typically consists of two shields with a magnetoresistive (MR) sensor positioned between the shields. Magnetic flux from the surface of the disc causes rotation of the magnetization vector of a sensing layer of the MR sensor, which in turn causes a change in electrical resistivity of the MR sensor. This change in resistivity of the MR sensor can be detected by passing a current through the MR sensor and measuring the voltage across the MR sensor. External circuitry then converts the voltage information into an appropriate format and manipulates that information as necessary.
The disc or other magnetic media is typically organized into tracks which are further organized into bit fields. The MR sensor is held in close proximity to the surface of the disc so that the sensor can be affected by the magnetic flux from each bit field within the disc. As the MR sensor travels along a track of the disc, any change in directionality of the magnetic flux between bit fields is detected by the MR sensor. The rotation of the magnetization vector with the change from one bit field to another results in the corresponding resistivity change and consequent voltage output from the MR sensor. Since it is the change from one bit field to another that is detected and results in the data output, it is critical that those transitions be sharp, that is, as narrow as possible. In other words, the domain wall between bit fields with opposite magnetization vectors will be as small in area as possible. Sharp transitions, as well as other characteristics for successful reading, are not controlled by the reader, but instead by the writer and the process used to encode the data within the magnetic media.
The writer typically consists of two magnetic poles separated from each other at an air bearing surface of the write head by a write gap. Additionally, the two magnetic poles are connected to each other at a region away from the air bearing surface by a back via. The magnetic flux path created by the two magnetic poles and back via is commonly called the magnetic core. Positioned between the two poles are one or more layers of conductive coils encapsulated by electrically insulating layers. To write data to the magnetic media, a time varying electrical current, or write current is caused to flow through the conductive coils. The write current produces a time varying magnetic field in the magnetic poles and across the write gap. A magnetic media is passed over the air bearing surface of the writer at a predetermined distance such that the magnetic surface of the media passes through the gap field. As the write current changes, the write gap field changes in intensity and direction.
The magnetic fringe field created by the writer gap causes and controls the write process. The cross sectional area of this writer gap is critical and determines the magnetic field strength. The cross-sectional area of the writer gap is defined by two parameters, the throat height and notch width. A very short throat height decreases the gap area and effectively increases the fringe field. A larger field allows the writer to activate the higher coercivity media that is necessary for high linear density recording. Control of the throat height is important for magnetic field control. Excessively short throat height can cause excessive magnetic flux density in the gap and create fringe field distortion. Dimensional control of the notch width is also important for reasons similar to those described for throat height control.
Recent years have seen a considerable increase in data storage densities. Generally, the storage capacity of a magnetic data storage and retrieval device is increased through use of magnetic media having an increased areal density. Areal density is the number of units of data stored in a unit area of the media. Areal density is determined by two components of the magnetic media: the track density (the number of data tracks per unit width of the magnetic media) and the linear density (the number of units of data stored per unit of length of the data track). To increase the areal density of a magnetic media one must increase the linear density and/or the track density of the magnetic media.
Increases in areal density have been achieved by: increasing the strength of the write gap field, decreasing the thickness of the gap between the magnetic poles at the air bearing surface, decreasing the width of the writer poles at the air bearing surface and increasing the coercivity of the magnetic media. These improvements require the material(s) of the magnetic core to conduct relatively high flux densities. Magnetic softness and well-defined anisotropy are properties of materials related to the ability to readily conduct magnetic flux.
Materials have a magnetic saturation level beyond which they will conduct no additional flux. Therefore each material has an intrinsic limit to the flux density that can be conducted. Consequently, it is desirable to incorporate high magnetic moment (HMM) materials because these materials can conduct a larger quantity of flux before reaching the point of magnetic saturation. The ability to conduct relatively high flux densities is especially desirable at those portions of the magnetic core or poles which are adjacent to the gap. Those portions, commonly called the pole tips, are critical for controlled and effective direction of the magnetic flux into the media.
In addition to the ability to conduct high flux densities, writer poles also need to avoid the formation of eddy currents. Eddy currents are induced through the magnetic core each time the write gap field changes directions. These eddy currents, which are counteracting to the flow of current from the change in direction of the write gap field, have a negative effect on the performance of the transducing head. First, the eddy currents act as a shield to prevent external fields from penetrating the magnetic core, thereby reducing the efficiency of the transducing head. Second, the increased eddy currents increase the time required to reverse the direction of magnetic flux through the magnetic core, thereby negatively impacting the data rate of the writer. Typically, eddy current effects can be minimized by increasing the resistivity of the material forming the magnetic core. Higher resistivity materials, however, generally have lower saturation moments and the high magnetic moment materials commonly have low resistivity.
Since it is difficult to find a material having the combined properties of a high magnetic moment, high permeability/low coercivity and a high resistivity, more recent prior art writers have used multiple materials to lend the combination of these properties to the writer. Frequently, prior art designs would focus on improving a single aspect of writer performance, for example reducing eddy currents. One such prior art approach is to form the magnetic core of two layers. One layer is formed of a high magnetic moment material and the other layer is formed of a material with a greater resistivity. But, the use of a multi-layer core will necessarily reduce the overall magnetic moment over that possible with a writer formed of solely high magnetic moment material.
A second prior art approach is to form a top pole of the magnetic core of two pieces: one piece of a high magnetic moment material and a second piece of a high resistivity material. This “two piece pole” (TPP) design originated from the need to build the pole tip separately from the pole yoke due to photo-processing concerns. Additionally, a bottom (or shared) pole of the magnetic core may be a recessed pole similarly formed of two pieces. In the case in which both the top and bottom pole are formed of two pieces, the build process of the writer would progress as follows: A planar second bottom pole piece would be deposited; a planar first bottom pole piece would be deposited on a portion of the second bottom pole piece; a write gap layer would be deposited over an exposed portion of the second bottom pole piece and the first bottom pole piece, a planar first top pole piece would be deposited over the write gap layer; a tri-layer stack formed of the first bottom pole piece, the write gap layer, and the first top pole piece would be shaped to define a pole tip region; insulating layers and coils would be deposited; and finally, a second top pole piece would be deposited over the first top pole piece, as well as over the insulating layers and coils. This build process is necessary because the first bottom pole piece and the second bottom pole piece need to be built on a flat surface to allow for proper shaping of the pole tips. Thus, the existing TPP structures all require stacking the first pole piece on the second pole piece, which is inefficient for flux transportation in addition to increasing the cost and complexity of the manufacturing process.
Accordingly, there is need for a high efficiency writer incorporating very high magnetic moment materials for use with high density magnetic data storage media.